manifest: use 't' for tree manifest flag
We currently use 'd' to indicate that a manifest entry is a
directory. Let's switch to 't', since that's not a valid hex digit and
therefore easier to spot in the raw manifest data.
This will break any existing repos with tree manifests, but it's still
an experimental feature and there are probably only a few test repos
in existence with 'd' flags.
$ hg init repo
$ cd repo
$ touch foo
$ hg ci -Am 'add foo'
adding foo
$ hg up -C null
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
this should be stored as a delta against rev 0
$ echo foo bar baz > foo
$ hg ci -Am 'add foo again'
adding foo
created new head
$ hg debugindex foo
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 0 ..... 0 b80de5d13875 000000000000 000000000000 (re)
1 0 13 ..... 1 0376abec49b8 000000000000 000000000000 (re)
$ cd ..